The Parasympathetic NS Flashcards
When is the parasympathetic NS most active?
when a person is relaxed and resting
What happens when the parasympathetic NS is active?
- heart beat and respiratory rate slow down
- peristalsis is active
- pupils constrict
- saliva is secreted
Where are postsynaptic parasympathetic neurons found?
in the organ itself (they go to surrounding areas and have no need to be as long as the presynaptic neurons)
What is the main neurotransmitter in the parasympathetic NS and what does it allow?
ACh to allow a much longer response
Where do most of the preganglionic parasympathetic NS neurons originate?
in the brainstem and sacral part of the spinal cord (CIII, VII, IX and X and S2-4)
What do the postganglionic parasympathetic NS neurons innervate?
- heart
- structures with smooth muscles
- glands
What are the 4 cranial nerves related to the parasympathetic NS?
- oculomotor (CIII)
- facial (CVII)
- glossopharyngeal (CIX)
- Vagus (CX)
What does the Vagus nerve do?
innervate the heart, lungs and all the abdominal viscera up to the left colic flexure (proximal 2/3 of the transverse colon)
What is the transverse colon?
the most mobile and longest part of the large intestine
Where are the preganglionic cell bodies of the Vagus nerve aggregated?
in the dorsal motor nucleus of the Vagus
Where are the postsynaptic parasympathetic cell bodies of the Vagus nerve located?
in the atrial wall and interatrial septum near the SA and AV nodes and along the coronary arteries
What does parasympathetic stimulation to the heart do?
- slow HR
- reduce force of contraction
- constrict coronary arteries to save energy between periods of increased demand
What does ACh in the heart do?
bind with muscarinic receptors to slow the rates of depolarisation of the pacemaker cells and AV conduction and decrease atrial contractility
Where do the parasympathetic fibres conveyed to the pulmonary plexus synapse?
- parasympathetic ganglion cells in the pulmonary plexuses
- along the branches of the bronchial tree
How does the Vagus nerve pass into the abdomen?
by piercing through the diaphragm together with the oesophagus to synapse with neurons in the walls of the GIT
What does the Vagus nerve supply in the walls of the GIT?
- stomach
- small intestine
- parts of the large intestine
What parts of the large intestine does the Vagus nerve supply?
ascending colon and proximal 2/3 of the transverse colon
What are the 2 main parts of the GIT innervated by the parasympathetic NS?
- submucosal plexus for secretion of digestive glands
- myenteric plexus for contraction of smooth muscles or peristalsis
What does the sacral parasympathetic outflow supply?
- distal third of the transverse colon
- descending colon
- genital and urinary systems
How do the axons reach the mural ganglia of the descending colon, ureter and genital organs?
they leave through the ventral roots and soon separate from the spinal nerve to form the pelvic splanchnic nerves
What does parasympathetic supply to the bladder cause?
contraction of the detrusor muscle in the wall for micturition (urination)
What does parasympathetic supply to the external genitalia cause?
increased blood flow into the cavernous spaces of the penis leading to erection in males and to clitoral engorgement in females
In which 5 nuclei are cell bodies of parasympathetic preganglionic neurons located?
- Edinger-Westphal nucleus
- Superior salivary nucleus
- Inferior salivary nucleus
- Lacrimal nucleus
- Dorsal motor nucleus of Vagus
Which cranial nerves correspond to which brainstem nuclei?
- Edinger-Westphal = eye via CIII
- Lacrinmal = lacrimal gland via CVII
- superior salivary = submandibular and sublingual glands via CVII
- inferior salivary = parotid gland via CIX
- dorsal motor = heart, lungs and GIT via CX
What happens as the preganglionic parasympathetic axons approach their destinations?
they synapse in specific ganglia before postganglionic neurons finally reach their target organs
Where does each parasympathetic cranial nerve synapse before reaching their target?
- CIII = ciliary ganglion
- CVII = pterygopalatine ganglion and submandibular ganglion
- CIX = otic ganglion
- CX = mural ganglia in GIT
What do postsynaptic fibres from the ciliary ganglion supply?
the sphincter pupillae and ciliary body in the eye
How does the sphincter pupillae change?
depending on light availability and relaxation state
When does the sphincter pupillae stretch and contract respectively?
- stretch when there is light in the eye or sympathetic innervation
- contract where there is less light or parasympathetic innervation
What are the lacrimal glands?
tear ducts of the eye responsible for cleaning and removing foreign objects
What supplies the lacrimal gland?
postsynaptic fibres from the pterygopalatine ganglion
Where are preganglionic neurons for the submandibular and sublingual glands located?
in the superior salivary nucleus
How does activation of the parasympathetic NS help with digestion?
secretion of saliva by the submandibular and sublingual glands as well as the parotid gland that contains amylase enzymes
Where do axons in the inferior salivary nucleus synapse?
in the otic ganglion
What are the sizes of the pre and postsynaptic neurons for the sympathetic and parasympathetic Ns?
- preganglionc SNS = short
- postganglionic SNS = long
- preganglionic PNS = long
- postganglionic PNS = short
